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The effect of rumen inert fat supplementation and protein degradability in starter and finishing diets on veal calf performance and the fatty acid composition of the meat

Lategan, Elna (2000-03)

Thesis (MSc)--Stellenbosch University, 2000.

Thesis

ENGLISH ABSTRACT: Six groups each with six Friesian bull calves were used in this investigation and slaughtered
at 20 weeks of age. Calves received a low- (LD) or high (HD) degradable protein diet, each
with or without rumen inert fat supplementation. Two commercial fat sources were used,
Morlae (m) and Golden Flake (gf), included at 2.5% of the diet. A commercial milk replacer
(Denkavit) was fed at 4L for 42 days, followed by 2L until weaning at 49 days of age. The
starter diets were fed ad lib. from day 14 to 10 weeks of age and finishing diets ad lib. from
11 to 20 weeks of age. There were no significant differences in body mass gain or dry matter
intake over the entire 20 week period. The feed conversion ratio (FCR) was improved
significantly (P=0.0032) when fat was supplemented to LD, but not to HD diets. The FCR
(kg dry matter/ kg gain) ofLD, HD, LDm, HDm, LDgfand HDgfdiets were 3.45,3.44,3.07,
3.81, 3.02 and 3.43, respectively. All 36 calves were used in a digestibility trial, using
chromium oxide (Cr203) as a marker, during week 18 of the investigation. Digestibility
values (%) for the six diets (LD, HD, LDm, HDm, LDgfand HDgf) were 61.74, 65.91, 75.44,
69.00, 75.54 and 67.15 for dry matter, 61.44, 61.60, 71.33, 68.23, 75.44 and 66.12 for crude
protein and 58.56, 66.45, 75.98, 70.92, 78.43 and 70.79 for fat, respectively. The dry matter
(P=O.OOOl)and fat (P=O.OOOl) digestibilities were only significantly higher when fat was
added to LD diets. The crude protein (CP) digestibilities were significantly higher when fat
was added to either the LD (P=0.0001) or the HD (P=0.0488) diets.
All the calves were slaughtered at 20 weeks of age and the fatty acid content of the meat (m.
longissimus) and subcutaneous fat layer adjacent to the 12th rib as well as the meat colour,
was determined. The fatty acid composition of the longissimus muscle was changed by
feeding the rumen inert fat sources. The three predominant fatty acids found were palmitic,
stearic and oleic acids. The palmitic acid (CI6:0) content of the muscle and diet was 24.44 &
20.47,25.97 & 22.57,31.06 & 33.23, 30.98 & 37.91, 34.94 & 31.77 and 29.71 & 32.88 of the
total fat for the LD, HD, LDm, HDm, LDgf and HDgf diets, respectively. The C16:0 content
was significantly higher in the muscle of the calves receiving the LD diets supplemented with
fat (P=0.0008). There was also a significant interaction between the two fat sources and
protein degradability (P=0.0065), but only in the LD diets. The stearic acid (CI8:0) content
of the muscle and diet was 14.35 & 5.22, 19.65 & 8.61, 17.29 & 4.68, 22.59 & 5.78, 22.27 &
15.54, and 26.48 & 20.15 of the total fat for the LD, HD, LDm, HDm, LDgfand HDgfdiets,
respectively. The C18:0 content was significantly higher in the muscle of calves receiving the
HD (P=O.OOOl)compared to LD diets. The stearic acid content was also significantly higher
when fat was added to LD (P=0.0042) or HD (P=0.0073) diets. The oleic acid (CI8:1)
content of the muscle and diet was 36.06 & 21.51,39.99 & 21.11,32.21 & 23.67, 29.13 &
24.59, 25.23 & 18.68 and 35.93 & 16.02 of the total fat for the LD, HD, LDm, HDm, LDgf
and HDgf diets, respectively. The linolenic acid (CI8:3) content of the muscle was
significantly higher (P=0.0038) when fat was added to LD diets compared to no fat
supplementation (0.87 vs. 0.15). The CIELAB values indicated that LD diets resulted in more
pink meat. Mean values ofL* =-32.61, 34.19; a* = 7.08, 7.91 and b* = 3.18 and 4.07 were
observed for the LD and HD diets, respectively. Meat from the LD diets had significantly
lower L*-(P=0.0252), a*-(P=0.0283) and b*-(P=0.0109) values compared to meat from the
HD diets. It was concluded that there was a positive response in CP digestibility when rumen
inert fats were supplemented to LD or HD diets, although a greater response was shown in the
LD diets. The FCR, dry matter and fat digestibility were only increased when fat was added
to the LD and not to the HD diets. Similarly, the fatty acid contents of the longissimus
muscle of veal calves can be manipulated with the supplementation of rumen inert fat sources,
but only when combined with a low protein degradable diet. The low degradable protein diets
also produce a more attractive meat colour for the potential veal consumer.